1. Field of the Invention
The present invention relates to a headlight apparatus for an automotive vehicle, and more specifically to a headlight apparatus which can control a headlight beam from high beam to low beam or vice versa by adjusting the angle of optical axis of the headlamp.
2. Description of the Prior Art
In general, the headlight apparatus for an automotive vehicle can be switched manually or automatically from high beam (used when the vehicle is running on a road where no opposed vehicle is running) to low beam (used when the vehicle is running on a road where an opposed vehicle is running or on a bright town or city road) or vice versa.
Japanese Published Unexamined (Kokai) Utility Model Application No. 60-61942 discloses an example of prior-art headlight apparatus by which low and high beams can be switched automatically.
In this prior-art headlight apparatus, there are provided a vehicle speed sensor for detecting its own vehicle speed and an other vehicle presence sensor for detection the presence of other vehicles such as opposed vehicles (running on an opposing lane in the opposite direction) and leading vehicles (running on the same lane in the same direction), and the angle of optical axis of the headlamp can be adjusted automatically according to output signals from the vehicle speed sensor, and further the adjusted angle of the headlamp optical axis is restricted in response to output signals from the other vehicle presence sensor. That is, in this prior-art headlamp apparatus, the optical axis of the headlamp is adjusted upward when the vehicle is running at high speed so that the headlamp reaches a long distance, but adjusted downward when the other vehicle presence sensor detects other opposed or leading vehicles so that the headlamp illumination distance can be shortened to prevent other vehicle's drivers from being dazzled.
In the above-mentioned prior-art headlight apparatus, the high beam can be adjusted so as to reach the maximum distance to a leading vehicle when an opposed vehicle is absent. However, when an opposed vehicle is detected by the other vehicle presence sensor, since sensor signals from the other vehicle presence sensor have priority over sensor signals from the vehicle speed sensor, there exists a problem in that there exists a certain non-sufficiently illuminated area between the headlight apparatus and a leading vehicle, in particular, when the vehicle on which the headlight apparatus is mounted is running at high speed.